This invention generally relates to vehicle engine controls. More particularly, this invention relates to a system and method for smoothing out engine performance under certain conditions.
Multiple cylinder vehicle engines are well known. The performance of the engine depends upon certain timing and other performance criteria issues. One problem that is common in vehicles is a roughness in engine performance at certain low levels, such as engine idle.
Engine roughness at engine idle or other low load conditions often results from imperfections in the engine components, which form the cylinders. Physical variations in the cylinders can result in variations in performance, which is especially noticeable at low level RPMs. Because the spark angle of each cylinder typically is set the same for all cylinders, any manufacturing differences results in less than ideal engine performance at low levels. The conventional way of attempting to address this problem has been to attempt to more tightly control manufacturing processes of the cylinders. Limitations on manufacturing tolerances, however, render this solution less than complete.
This invention provides a unique solution to the problem of controlling rough engine performance at low engine output levels.
In general terms, this invention is a system and method for controlling the performance of a vehicle engine. A performance characteristic of each cylinder is monitored with the engine performing at a low output level. The preferred engine performance characteristic is the indicated mean effective pressure. Whenever a rough engine condition exists, a determination is made about which of the cylinders is performing differently than the others. Whenever one cylinder, for example, has a lower indicated mean effective pressure than the other cylinders, that cylinder performance is adjusted. In one example, the spark angle of the cylinder performing differently is adjusted to bring that cylinder performance to a level that is consistent with the other cylinders.
In some situations, more than one cylinder is adjusted. It is also possible within the scope of this invention to adjust the performance variable upward or downward to bring the performance of the different cylinder into alignment with the majority of other cylinders.
The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows.